Large volume submersible pumps, commonly used in oil well production, have a submersible electrical motor that rotates a shaft. The shaft extends through a seal section into a centrifugal pump for rotating the pump. In the seal section, there are several partitions through which the shaft passes. At the entrance and exit of the seal section and in the partitions, mechanical face seals are mounted to seal the interior from exterior well fluid.
A typical mechanical face seal has an annular stationary member that is mounted to the wall structure. A rotating seal member is coupled to the shaft to rotate with the shaft. The rotating seal member has a face that is urged into contact with the stationary face by means of a coil spring. Normally, the rotating seal member is not rigidly mounted to the shaft, rather is mounted by means of a elastomeric barrier and coil spring.
Although not rigidly mounted, the rotating seal member will vibrate radially to some extent if the shaft is out of alignment due to wear on the sleeve bushings. The radial movement of the rotating seal face against the stationary face reduces the life of the seal.